Need some help with Type-B...size and wye

[SJoseHomer]

Hello...hope the HVAC experts here can help with some questions. Just joined and this is my first post. Please bear with the length and detail.

While researching a replacement blower motor for furnace, I discovered the vent pipes in our garage are single-wall, and actually go through a drywall ceiling. The garage is not conditioned; it simply has drywall hung and taped. The hole is just about the size of the 6" vent pipe. By reading up on the issue, I found single-wall needs 6 inches from any combustibles. I definitely don't have that. I do not see any burn or scorch marks on the drywall, in the crawl space, or on any joists near the vent stack in the crawl space, or plywood roof. No insulation is near it either. Even so, I embarked on figuring out what to do to replace with Type-B vent, that only requires 1 inch clearance and is to code.

I have two appliances feeding the main vent stack...nat gas furnace and a water heater...connected by way of elbows, TEE, and increaser adapter. Again, all single-wall. The furnace is an old York Diamond 80 P3DNB16 rated for 64,000 BTUs, while the water heater is a newer A.O. Smith rated at 40,000 BTUs (potentially combined 104,000 BTU output). The furnace has a 4" vent, and the water heater a 3" vent. The main stack, which appears to be 6", is almost directly above the furnace, so it serves as the larger and primary vent line. The water heater is what connects to the TEE. Also, it sits next to the furnace, with the water heater vent cap center about 18" from the center of furnace vent. The entirety of the vent pipe run is relatively short...the distance from the top of the furnace to the ceiling is about 30" and the run from ceiling to roofline in the crawlspace is about 42" (total run from furnace to outside is about 80"). And again, it's primarily vertical. see attached diagram.

My current plan is to use rigid Type-B throughout:
- connect water heater by using a 3" appliance connector to a 3" 45 degree elbow to create angle, run 3 foot 3" pipe to WYE.
- connect furnace by using 4" appliance connector to 4" 90 degree elbow to create appropriate angle, and then to WYE.
- WYE would be 4" x 3" x 4".
- connect 4" to 5" increaser to top of WYE, so it can connect to new 60" Type-B 5" pipe, that would run up through the drywall ceiling, crawl space, and out through the roof.
- use fire stop support plates...one on the drywall ceiling, and also one up in the crawl space where pipe stack feeds through to insure insulation space clearance.
- install short 2x4 supports in crawl space to attach pipe support hangers, and then attach to Type-B pipe...careful to keep 1" distance from pipe.

So, my questions...

1. Is a 5-inch Type-B main stack after the WYE large enough to handle the potentially combined 104,000 BTUs output? I have reviewed some charts and graphs but cannot decipher best size to go with...5" or 6"? Are there advantages or disadvantages to using one or the other? I would use an increaser to get from the 4-inch WYE to the new 5" or 6" main stack. Honestly, 5" components are much easier to locate at supply houses in my area, so if either is acceptable I would go with the 5".

2. Is the WYE connector supposed to be "single-wall"? The connector I purchased (Amerivent 4FCY-3) looks like it does not have, nor designed to have, an internal aluminum pipe. It does have the Type-B connector collars. Is there an actual "double-walled" WYE made by a manufacturer? Does this connection from water heater to furnace main line have to be a WYE? Can it be a double-walled TEE? I have seen many diagrams illustrating TEE's used in this method. But I have heard it's best to use a WYE to prevent furnace gases from possibly "back-flowing" into and down the water heater line, and out the vent cap. True?

3. Also, the 45 degree, 3-inch joint on the WYE does not seem to be completely "sealed". The joint is well connected mechanically, but holding it up I can see light coming through the sides where the 3-inch pipe meets the main 4-inch body, which concerns me that it is not "vapor-tight". Is there a high temperature sealant that needs to be applied to prevent gases from seeping out through the sides of the joint? I was looking at a 3M Fire Block Sealant FB 136 as a possibility. Or DAP Hi Temp RTV Silicon Sealant? Or, does the the WYE "intentionally" have this "un-sealed" design, to promote adjacent air to be sucked in and aid with uplifting gases? Should the WYE connection joint not be sealed and left as-is? No hi-temp metal tape?

4. Can the single-wall WYE be used in the middle of the run? I read single-wall can only be used connecting appliance to the vent run, and not in the middle. For example, you can't go double, to single, to double. Using a WYE in the design I am thinking of would obviously put it in the "middle".

Please see the attached pics...one of the current installation and one of a drawing I made with pertinent information.

If anyone can provide guidance on these questions and feedback on my hopeful design, please respond.

Much thanks!

 

[readhead]

It appears that the pipe going through the ceiling is B vent. For the time, guessing ‘50’s-60’s, that was a normal installation and still is in many locations. Since you are concerned about clearance you can cut the drywall back 1” and install a metal draft stop on the ceiling, seal the rest of the pipe joints and call it a day.

 

[FMB4]

Welcome aboard SJoseHomer.

 

[Jackfre]

The rule on the use of single wall as a vent connector is that you can run up to[ 1.5’/inch diameter of pipe. So 4” pipe gives you a max of 6’ of single wall VC. Your system is piped correctly. It isn’t pretty and could be improved with an insulated VC, B-vent, but if the system is not showing problems, I’d find other things to do. My statement presumes that the main stack ips B-vent all the way up.

 

[danski0224]

All of the Type B vent manufacturers have something odd on their websites... Installation Instructions... and charts.

 

[SJoseHomer]

It appears that the pipe going through the ceiling is B vent. For the time, guessing ‘50’s-60’s, that was a normal installation and still is in many locations. Since you are concerned about clearance you can cut the drywall back 1” and install a metal draft stop on the ceiling, seal the rest of the pipe joints and call it a day.

Really? I could have swore it was single-wall. Where the adapter joins into the 6", I only see single edge sheet metal. I guess the easiest way is to remove the cap from the roof, and look at the top edging before breaking this build down.

The house was built in '82, i believe. And I'm sure houses in our subdivision when sold as new did not have finished garages. Many neighbors still have bare studs.

 

[SJoseHomer]

And thanks for the welcome!!!

 

[readhead]

The dimples in the pipe indicate that it is B vent. They space the inside pipe from the outside. I just looked at the picture again and noticed that all the pipe to the furnace is installed backwards. It should be lapped so that any condensation flows down the pipe and not out of the joints.

 

[SJoseHomer]

Yessssirr, Redhead...you are right...it is B-vent. Took a very close look and I can see the inner wall at the TEE connection point. But the TEE and the two elbows appear to be single-wall.

I'm a bit confused by "installed backwards" and "lapped". Currently the elbows connected to the furnace exhaust stack are male-lower going into female-upper. That's not correct with single-wall? Gas in this install method I would think flows over the joint, not into it. By condensation, do you mean water forming inside the venting, or outside and running down to the top of furnace? Never had an issue as far as I know with condensation "outside" the vent pipes.

I have no problem removing it all and replacing with new B-vent with the correct twist-lock connections and direction...just want to make sure it's done right. Who knows how dirty that old venting is on the inside. I have had the furnace serviced periodically and it seems in good shape, but doubt the techs opened-up the upper venting and vacuumed/cleaned. I'm leaning towards replacing it all with the final run through the ceiling being 5". You all think that size is okay? Or maybe keep the final 6" run and replace everything below.

My biggest question is the connection point between the furnace and water heater; the WYE...the "unsealed" joint. Anyone know if this is intentional on the part of manufacturer to aid in updraft? Or should it be sealed?

Installing it instead of the TEE would provide a 45 degree angle to prevent furnace exhaust from possibly flowing back down and out the water heater vent cap. But just by looking at the height of where the connection would be made closer to the ceiling, using a double-walled TEE and then using a 45 elbow to begin the 3" downward run to the WH would still provide, I think, the proper descent angle to prevent the back flow, correct? Would that be proper?

If I can get that main question answered I can start the job.

The reason I'm in this situation is the furnace blower motor seems to have failing bearings. Running the fan produces an awful whine in the furnace enclosure. I bought the correct replacement motor, but got held up with replacement installation when I discovered my style furnace is down-draft and has the exhaust running in front of the blower enclosure. Burner assembly is on the bottom half of the furnace while the blower is on the top half. To remove the motor, I have to disassemble the stack inside that runs from the bottom to top, and at least the elbows just above. If the furnace model was an "up", I never would have thought about the vent stack, B-vent, clearances, etc. I guess it's a blessing there.

Thought about calling in an HVAC company but cringe that they will probably charge me $400-$500 for a job I'm sure I can do, with the right materials and guidance.

Thanks to you all for your insight and help.

 

[readhead]

Condensation forms when the flue gases cool in the flue pipe. When the condensation forms and flows down the inside of the pipe it would come out at the joints when the pipe is installed the way it is on your furnace. If you look at the joints on B vent the inner and and outer walls both lap so that moisture will flow from top to bottom. Condensation on the inside and rain on the outside.
The distance to the vent cap is pretty short so condensation hasn’t been an Issue.
You seem to be trying to solve a problem you don’t have. Everything has performed fine for thirty nine years. Take it apart, install the motor and put it back together. I would tape the joints and current code requires screws in the joints.

 

[brewchief]

Vent connection direction is proper for a gas vent, wood stove they need to go the other way. If you have condensation forming that doesn't go away in a few minutes at most then you have other problems. You are better off having a straight piece on top of the water heater going up at least a foot then the horizontal piece keeping a 1/4" per foot slope up. I very rarely use any 3"pipe for vents, 99% of the water heaters we do get a 4" vent connector.

 

[SJoseHomer]

Thanks gents...appreciate the info. If you need advice in the A/V world, I may have a thought or two.